Method of manufacturing a cold plate heat exchanger assembly having a metallic compliant gasket

ABSTRACT

The subject invention provides a method of manufacturing an all-metal cold plate heat exchanger assembly for removing excess heat from a heat generating electronic component. The cold plate assembly includes a base plate having micro-channels and associated micro-fins, a manifold plate having alternating channels, and a manifold cover, wherein the manifold plate cooperates with the micro-channels to form an engineered pathway for coolant flow. This method assures a tight interface sealing between the contact surfaces of the alternating channels of the manifold plate and the coplanar surfaces of the micro-fins that would prevent coolant by-pass flow, but without clogging or jeopardizing the flow through the micro-channels. This method utilizes a layer of recast metallic particulates, which is a natural by-product of laser machining, as a compliant gasket material between the coplanar edges of the alternating channels and the coplanar edges of the micro-fins.

TECHNICAL FIELD OF INVENTION

This invention relates to a method of manufacturing an all-metal cold plate heat exchanger assembly.

BACKGROUND OF INVENTION

Forced air-cooling is typically used to remove excess heat generated by computing processing units (CPUs); however, forced air-cooling alone is no longer sufficient to meet the cooling needs of increasingly faster and hotter CPUs. An alternate to forced air-cooling is a recirculating closed-loop liquid cooling system. Recirculating closed-loop liquid cooling systems are known for their higher efficiency and capacity for excess heat removal.

A schematic of a typical recirculating closed-loop liquid cooling system for cooling a heat generating electronic component is shown in FIG. 1. Illustrated is a recirculating closed-loop liquid cooling system 10 that includes a reservoir tank 15, a coolant pump 22, a cold plate heat exchanger assembly 25, a radiator 35, and a fan 40. The cold plate heat exchanger assembly 25 is in thermal conductive contact with the heat generating electronic component 30. It is understood that the heat generating electronic component 30 can represent a CPU.

The coolant pump 22 transfers a liquid coolant from the reservoir tank 15 to the cold plate heat exchanger assembly 25. Within the cold plate heat exchanger assembly 25 are engineered flow channels, which provide a tortuous path for flow of liquid coolant in order to optimize heat transfer from the heat generating electronic component 30 to the coolant. After exiting the cold plate heat exchanger assembly 25, the heated coolant continues to the radiator 35 where the heat is released to the ambient air by convection with the aid of a fan 40 blowing a stream of cooler air across the radiator 35. The cooled coolant then returns to the reservoir tank 15 to repeat the heat transfer process.

U.S. patent application Ser. No. 11/221,526 discloses an all-metal cold plate heat exchanger assembly with engineered flow channels. The disclosed cold plate assembly includes a base plate of copper having a flat exterior surface that is adapted to thermally bond to a heat generating electronic component. Located on the interior surface of the copper base plate are a series of micro-channels and associated micro-fins with coplanar edges. The base plate is assembled to a manifold cover and the interior surface of the manifold cover has manifold channels with corresponding co-planer surfaces that cooperate with the smaller coplanar edges of the micro-fins to define a path for coolant flow.

When the manifold cover is engaged to the base plate, the coplanar surfaces of the manifold channel are in intimate contact with the coplanar edges of the micro-fins of the base plate forming a checkerboard pattern for fluid flow, providing more effective and efficient heat extraction. The contact between the coplanar surfaces of the manifold channels and the coplanar edges of the micro-fins must be sufficiently tight, to prevent flow from bypassing the manifold channels, which would impair the regularity of the flow pattern and result in reduced heat transfer efficiency.

One known method of manufacturing a cold plate assembly having good sealing characteristics between the contact surfaces of the manifold channels and the micro-fins is to utilize materials such as solder, braze cladding, or adhesives to provide a gasket material between the coplanar surfaces of the manifold channels and the coplanar edges of the micro-fins. A drawback for such materials is the tendency during the assembly process for such materials to seep into and clog the micro-channels.

Another known method of manufacturing a cold plate assembly having good sealing characteristics between the contact surfaces of the manifold channels and the coplanar edges of the micro-fins is resistance welding, which is disclosed in U.S. patent application Ser. No. 11/221,526. The drawbacks to resistance welding are the cost of materials and complexity of the manufacturing operation. Resistance welding requires the use of highly pure, oxygen free copper that is both electronically and thermally conductive. In addition to the material requirements, the joining surfaces of the cold plate assembly require precision machining to exact specifications.

There exists a need for an economical method of manufacturing an all-metal micro-channel cold plate heat exchanger assembly that assures a tight interface seal between the contact surfaces of the manifold channels and the micro-fins without clogging the micro-channels.

SUMMARY OF THE INVENTION

The subject invention provides a method of manufacturing an all-metal cold plate heat exchanger assembly for removing excess heat from a heat generating electronic component. The method assures a tight interface seal between the contact surfaces of the alternating channels of the manifold plate and the coplanar edges of the micro-fins which prevents coolant by-pass flow, but does not clog or jeopardize the coolant flow through the micro-channels, and is economical to manufacture and assemble. This method utilizes recast metallic particulates, a natural by-product of laser machining, as a compliant gasket material between the coplanar surfaces of the alternating channels and the coplanar edges of the micro-fins.

The method includes providing a base plate formed of a material suitable for laser machining, preferably copper. A beam of laser energy is provided to machine alternating substantially parallel micro-channels and associated micro-fins into the interior surface of the copper base plate. During the laser machining process, the laser-machined surface of the copper base plate is vaporized into microscopic aerosol particulates, which are then cooled and condensed onto the coplanar edges of the micro-fin to form a layer of recast metal. The recast layer is microscopic and cannot be seen without magnification.

A manifold cover and a manifold plate, which may be integrated with the interior surface of the manifold cover, are provided. The manifold plate has alternating inlet-outlet channels with at least one face having coplanar edges. The manifold cover is arranged onto the base plate with the manifold plate in between, such that one face of inlet-outlet channel coplanar edges is disposed adjacent to the micro-fin edges with the recast layer in between. The manifold cover is then pressed toward the base plate to compress the recast layer to form a compliant gasket between the contact surfaces of the alternating inlet-outlet channels and micro-fins. The exterior joining surfaces of the base plate and manifold cover are hermetically sealed.

One advantage of the present invention is that it utilizes the vapor-deposited copper particulate that is a natural by-product of the laser machining process used in the formation of the micro-channels to form a compliant gasket that facilitates the intimate contact between the micro-channels and the manifold channels, thus preventing flow by-pass and increasing thermal performance.

Another advantage of the present invention is the elimination of the need to remove the recast layer prior to assembly; this, simplifies the manufacturing process and reduces cost.

Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of the preferred embodiment of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

This invention will be further described with reference to the accompanying drawings in which:

FIG. 1 is a schematic diagram of a closed-loop liquid cooling system for removing heat from a heat producing electronic component.

FIG. 2 is an exploded perspective view of the various components of a cold plate heat exchanger assembly.

FIG. 3 is a perspective view of the bottom of the manifold cover with an integrated manifold plate.

FIG. 4 is an enlarged perspective view of a portion of the bottom surfaces of the manifold plate's channels crossing the top edges of the micro-fins.

FIG. 5 is a schematic view of the flow pattern enabled by the completed cooling assembly.

FIG. 6 is a cross section of the base cold plate as micro-channels are being machined onto the interior surface.

FIG. 7 is an enlargement of detail circle shown in FIG. 6 showing a layer of recast metallic particulates on the coplanar edges of the micro-fins.

FIG. 8 is a portion of the cold plate having a layer of recast metallic particulate materials on the coplanar edges of the micro-fins as the manifold cover is pressed onto base plate.

FIG. 9 is an enlargement of detail circle shown in FIG. 8 showing the recast metal deforming and forming a compliant gasket between the top edges of the micro-fins and bottom surfaces of the manifold channels.

DETAILED DESCRIPTION OF INVENTION

In accordance with a preferred embodiment of this invention, referring to FIGS. 1 through 9, shown is an all-metal micro-channel cold plate assembly. The cold plate assembly utilizes what is normally an undesirable by-product of laser machining, a layer of recast metallic particulates, as a compliant gasket between the contact surfaces of the top edges of the base cold plate micro-fins and bottom surfaces of the manifold channels.

In reference to FIG. 2, shown is an exploded view of a preferred embodiment of the current invention, which is indicated generally at 20. The primary components of the cold plate assembly 20 are a base plate 100, a manifold cover 200, a manifold plate 300, and inlet/outlet pipes 400. Manifold plate 300 is shown as a separate component; however, manifold plate 300 may be manufactured as an integral part of the interior face 210 of manifold cover 200. All components are manufactured of a heat conducting metal, preferably pure substantially oxygen free copper. The components are assembled into an integral unit where the jointing surfaces are hermetically sealed by methods known in the art for joining metallic components that include, but not limited to, brazing, welding, chemical bonding, or resistance welding.

Base plate 100 is substantially circular in shape and is approximately 34 mm in outer diameter with a thickness of approximately 1.0 mm. Base plate 100 has a perimeter wall 110 that is approximately 3.0 mm in height demarcating an inner surface 120 from outer surface 130 of base plate 100. Inner surface 120 and outer surface 130 are machined to a high degree of flatness. Outer surface 130 is adapted to be thermally bonded to a heat producing electronic component. Inner surface 120 is laser machined to form a fin-channel pattern 135 that includes a dense pattern of extremely thin structures, alternating micro-channels 140 and micro-fins 150. These are shown in greater detail in FIG. 4. Fin-channel pattern 135 is substantially rectangular in outline and measures approximately 17 mm by 24 mm. In laser machining fin-channel pattern 135, a beam of laser energy is used to cut the pattern of micro-channels 140 and micro-fins 150. Shown in FIGS. 6 and 7, micro-channels 140 are approximately 350 to 450 microns deep and approximately 60 microns wide. Micro-fins 150 have substantially flat coplanar edges 160 that are approximately 50 microns in width.

Manifold cover 200 is also substantially circular in shape having an outer diameter of approximately 42 mm and is approximately 2 mm thick. Manifold cover 200 is adapted to engage perimeter wall 110 of base plate 100 and form a hermetically sealed structure. Located between the inner surface 120 of base plate 100 and interior face 210 of manifold cover 200 is a manifold plate 300, which may be formed as an integral part of interior face 210 of manifold cover 200 as shown in FIG. 3. Also attached to manifold cover 200 are inlet/outlet pipes 400, which may be composed of the same materials as manifold cover 200 and base plate 100. The joining surfaces of inlet/outlet pipe 400 are joined to manifold cover 200 by suitable methods such as welding or brazing.

In reference to FIGS. 3 and 4, manifold plate 300 includes a sinuous wall 310 that forms a substantially rectangular pattern measuring approximately 14 by 21 mm, which is slightly smaller than fin-channel pattern 135. The rectangular shape of manifold plate 300 is formed by the natural shape of sinuous wall 310 as it alternates forming a regular pattern of side-by-side alternating channels 320. Sinuous wall 310 has opposing faces of coplanar surfaces 330 that are approximately 0.44 mm in width, and the width of the corresponding channel is approximately 0.50 mm.

In reference to FIG. 3, one face of coplanar surfaces 330 may be integral with interior face 210 of manifold cover 200 while the opposing face of coplanar surfaces 330 is exposed. The exposed coplanar surfaces 330 are substantially parallel to coplanar edges 160 of micro-fins 150 on base plate 100 and are adapted to be positioned to engage coplanar edges 160 in a crossing pattern. The height of sinuous wall 310 is approximately 2.0 mm, which is substantially the same as the interior distance between inner surface 120 of base plate 100 and interior face 210 of manifold cover 200, when assembled, to provide close mechanical contact between coplanar surface 330 of manifold plate 300 and coplanar edges 160 of micro-fins 150 without significant bending or deformation of micro-fins 150. To prevent by-pass leaks created by less than solid contact between coplanar surfaces 330 and coplanar edges 160, a compliant gasket is applied, which will be discussed herein below in detail.

In reference to FIG. 5A, once the manifold cover 200 is assembled to base plate 100 with manifold plate 300 there between, the coplanar surfaces 330 of manifold plate 300 are in intimate contact with coplanar edges 160 of micro-fins 150 forming a checkerboard flow pattern. Coolant enters into alternating channels 320 of manifold plate 300 indicated by “X”, then down into the micro-channels 140 to flow under and across coplanar surfaces 330, and then exits up into adjacent alternating channels 320 of manifold plate 300, indicated at ‘O’, towards the outlet.

As discussed herein above, inner surface 120 of base plate 100 is machined to a high degree of flatness. The inner surface 120 is then laser machined to form a fin-channel pattern 135 that includes a dense pattern of extremely thin structures that include micro-channels 140 and micro-fins 150, which have corresponding coplanar edges 160 that are substantially planer to inner surface 120. In reference to FIGS. 6 and 7, the vaporized metallic particles from the laser machining process are controlled so as to condense and remain on the coplanar edges 160 of micro-fins 150 to be used as a compliant metallic gasket 510 as shown in FIGS. 8 and 9; the method of which will be discussed herein below.

The process of laser machining micro-channels onto a flat metallic surface is generally known in the art. As a high-powered laser is focused on a targeted material, the mass of the material is removed by vaporization caused by the intense heat generated by the laser beam at the point of contact. The amount of material removed is determined by the pulse duration, energy, and wavelength of the laser, as well as by the number of passes by the laser beam. These variables can be controlled according to the need of the material targeted to be removed. The desired setting of the laser should be adequate to remove the material by vaporization and not so high as to cause liquid ejection or phase explosion of the targeted material.

In reference to FIG. 6, a beam of laser energy 520 from a laser device 560 is provided to cut substantially parallel micro-channels 140 into inner surface 120 of base plate 100 in a predefined fin-channel pattern 135. When a pulse of laser energy 520 makes contact with inner surface 120, the extremely high-energy input ablates the metallic base plate 100 at the point of contact by vaporizing the metallic mass into a plume 530 of aerosol microscopic particulate matter 540. An inert blanket gas (not shown), such as nitrogen, is typically used to cover the surface of the work piece to prevent oxidation of the work piece and to cool plume 530, thereby assisting in controlling the rate of precipitation of the microscopic particulate matter 540.

The blanket of inert gas cools plume 530 as it expands outward. The aerosol particulate matter 540 collides with each other and coalesces into larger particulates in the range of nanometers. The larger particulate matter condenses and settles onto the coplanar edges 160 of the micro-fins 150 forming a layer of recast metal. Contrary to the teachings of the prior art to use an acid solution to remove the recast layer, the recast layer is allowed to remain on top of the coplanar edges 160 of micro-fins 150. Recast layer 500 consists of the same metallic material as base plate 100 and is at a consistency that is malleable enough to form a compliant gasket 510 between coplanar edges 160 of micro-fins and coplanar surfaces 330 of manifold plate 300.

As discussed herein above, it is critically important to insure intimate contact between the coplanar edges 160 of micro-fins 150 and coplanar surfaces 330 of manifold plate 300 to prevent fluid bypass. The recast layer 500 aids in the critical seal by deforming on a microscopic level to average out any inconsistencies in the micro-channel peak-to-peak dimensions and facilitates the required intimate contact.

The height and percentage coverage of the recast layer can be controlled by varying the intensity of the laser, temperature of the inert cover gas, and duration of cut. It is preferable that the temperature is below the dew point of the vaporized metallic particulates.

The height of the recast layer 500 is defined by the distance between the coplanar edges 160 of micro-fins 150, which is substantially planar with inner surface 120 of base plate 100, and plateau 550 of recast layer 500 shown as distance ‘X’ in FIG. 7. The ratio of coverage is defined by the width of coplanar edge 160 of micro-fin 150 that is occupied by recast layer 500, indicated as distance ‘A’, divided by the total width of coplanar edge 160 shown as ‘B.’ The optimum height ‘X’ of the recast layer 500 on the micro-fins coplanar edges 160 is determined through laboratory analysis and testing to be approximately 30 to 64 microns; and the preferred ratio of coverage is 0.3 to 1.0. Any height greater than 64 microns may result in the excess recast layer 500 deforming into micro-channels 140 to obstruct coolant flow.

Once recast layer 500 has been formed on coplanar edges 160 of micro-fins 150, a manifold cover 200 having a manifold interior face 210 and manifold plate 300 is arranged over base plate 100, with the channels 320 of manifold plate 300 substantially perpendicular to micro-channels 140 of base plate 100. Manifold cover 200 is then positioned onto base plate 100 such that the coplanar surfaces 330 of manifold plate 300 are disposed adjacent to the micro-fin coplanar edges 160 with recast layer 500 in between. Manifold cover 200 is pressed toward base plate 100 to compress recast layer 500 to form a compliant gasket 510 in between.

The exterior joining surfaces of the base plate 100 and manifold cover 200 are hermetically sealed by any of the known methods in the art; however, brazing is preferable. At temperatures favorable to brazing, recast layer 500 becomes more ductile and lends itself readily to act as a conformable layer to reduce fluid bypass.

While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow. Dimensions are only presented to illustrate the diminutive size of cold plate heat exchanger assembly 20 and are not intended to be limiting. Those skilled in the art can adjust the dimensions of cold plate assembly 20 to accommodate specific heat transfer requirements.

Furthermore, the function of cold plate assembly 20 has been described as removing excess heat from a heat generating electronic component; those skilled in the art can recognize that cold plate assembly 20 can also function by adding heat to a component by pumping preheated coolant through the cold plate assembly 20.

Still furthermore, cold plate assembly has been described as being all-metal. Those skilled in the art can substitute alternative materials other than metal for components that are not crucial to the making or using of the present invention. Therefore, it will be understood that it is not intended to limit the method of the invention to just the embodiment disclosed. 

1. A method of manufacturing a cold plate heat exchanger assembly for a heat-producing component, comprising the steps of: providing a base plate formed of a material suitable for laser machining, wherein said base plate has an interior surface that is substantially planar; providing a manifold cover; providing a manifold plate having alternating inlet-outlet channels, wherein said inlet-outlet channels have coplanar surfaces; laser machining a pattern of alternating substantially parallel micro-channels and micro-fins into said base plate interior surface, wherein each of said micro-fins have a micro-fin edge, and wherein said laser machining includes controlling laser energy and ambient temperature to produces aerosol particulate matter that rises from said micro-channels and deposits onto said micro-fin edges to form a recast layer; arranging said cover manifold onto said base plate with said manifold plate in between such that said inlet-outlet channel coplanar surfaces are disposed adjacent to said micro-fin edges with said recast layer in between; pressing said manifold cover toward said base plate to compress the recast layer to form a compliant gasket in between; and hermetically sealing said base plate to said manifold cover.
 2. The method of manufacturing a cold plate assembly of claim 1 wherein the step of said laser machining further comprises the steps of: blanketing said base plate interior surface with an inert cover gas having a predetermined temperature below dew point of said vaporized base plate material; and focusing and maneuvering a laser beam onto said base plate interior surface, wherein said laser beam has sufficient intensity to vaporize said base plate material into said aerosol particulate matter, thereby forming said micro-channels and said micro-fins; wherein said vaporized base plate material rises from said micro-channels into said cover gas and condenses into micro-droplets, which then deposit onto said micro-fin edges to form said recast layer.
 3. The method of manufacturing a cold plate assembly of claim 1, wherein said recast layer has a height less than 65 microns.
 4. The method of manufacturing a cold plate assembly of claim 3, wherein said recast layer has a height in the range 30 to 64 microns.
 5. The method of manufacturing a cold plate assembly of claim 1, where said recast layer has a coverage ratio in the range 0.3 to 1.0
 6. The method of manufacturing a cold plate assembly of claim 1, wherein said manifold plate is formed integrally with manifold cover.
 7. The method of manufacturing a cold plate assembly of claim 1, wherein said base plate is formed of copper.
 8. A method of manufacturing a cold plate heat exchanger assembly for an electronic component, comprising the steps of: providing a base plate formed of copper, wherein said base plate has an interior surface that is substantially planar; providing a manifold cover and alternating inlet-outlet channels, wherein said inlet-outlet channels have coplanar surfaces; providing a blanket of inert cover gas on to said base plate; laser machining a pattern of alternating substantially parallel micro-channels and micro-fins into said base plate interior surface, wherein each of said micro-fins have a micro-fin edge, and wherein said laser machining includes controlling laser energy to produce aerosol particulate matter that rises from said micro-channels into said cover gas and controlling temperature of said cover gas so that said aerosol particulate matter condenses onto said micro-fin edges to form a recast layer; arranging said cover manifold onto said base plate such that said inlet-outlet channel coplanar surfaces are disposed adjacent to said micro-fin edges with said recast layer in between; pressing said manifold cover toward said base plate to compress the recast layer to form a compliant gasket in between; and hermetically sealing said base plate to said manifold cover.
 9. The method of manufacturing a cold plate assembly of claim 8, wherein said recast layer has a height in the range 30 to 64 microns.
 10. The method of manufacturing a cold plate assembly of claim 9, where said recast layer has a coverage ratio in the range 0.3 to 1.0.
 11. The method of manufacturing a cold plate assembly of claim 10, wherein said coplanar surfaces of said inlet-outlet channels are in intimate contact with coplanar edges of micro-fins forming a checker board flow pattern. 